High conductivity thermostat



Oct. 29, 1957 H. w. BLETZ 2,811,610

HIGH CONDUCTIVITY THERMOSTAT Filed Feb. 27,f 1956 IN V EN TOR.

HOWARD W BLETZ ATTORNEYS United. rates Patent HIGH C(JNDUCTIVITY THERMOSTAT Howard W. Bletz, Lexington, Ohio, assignor to Stevens Manufacturing Company, Inc., a corporation of Ohio Application February 27, 1956, Serial No. 567,832

14 Claims. (Cl. 233-438) The invention relates in general to condition responsive devices and more particularly to temperature responsive devices such as thermostats containing a temperature responsive element which, by utilizing a high conductivity metal, is placed in good heat exchange relationship with an appliance or other unit to which the condition responsive device is attached or used.

A specific embodiment of the invention is that it may be used in a thermostat incorporating a bimetallic element with the thermostat carrying electrical contacts for on-off control of an electrical heating appliance to which the thermostat is mounted. In many forms of thermostats the various elements or members therein are held together by a rivet which typically has been made of steel for strength to resist the tension forces therein when the thermostat is assembled and also to resist the compression forces therein when the thermostat is mounted to the appliance. Such rivets have in the past utilized a steel head which is integral with the shank of the rivet and which head is placed between the temperature responsive element, such as a bimetal, and the mounting surface of the appliance. This steel head has inferior heat conducting properties.

Therefore, an object of the invention is to incorporate in a thermostat a metal of high conductivity such as aluminum or copper to readily conduct heat from the appliance to the thermostat.

Still another object of the invention is to provide an aluminum washer as a part of a composite head on a rivet for a thermostat wherein the aluminum washer is in contact both with the bimetallic element of the thermostat and the mounting surface of the appliance being controlled by the thermostat, yet the rivet shank remains of steel for supplying the required strength.

Still another object of the invention is to provide good heat transfer from the appliance to the bimetallic element of the thermostat.

Still another object of the invention is to provide a thermostat having a smaller operating temperature differential, between open and closed conditions of the electrical contacts of the thermostat, than prior art thermostat.

Still another object of the invention is to provide a thermostat mounting rivet with a composite head wherein a part of the head is integral with the shank of the rivet of high strength metal and another part is formed of a high conductivity metal, with the two parts having complementary interfitting surfaces and both parts being substantially coplanar to rest upon the mounting surface of the appliance to which the thermostat may be attached.

Other objects and a fuller understanding of this invention may be had by referring to the following description and claims, taken in conjunction with the accom-- 37 on the high conductivity washer 32. Also, the axial "ice Figure 2 is an enlarged sectional elevational view of the stack of the thermostat; and

Figure 3 is an exploded view of the composite rivet before assembly.

The thermostat 11 shown in the drawing is illustrative of one form of the invention which may be applied to a condition responsive device, and especially one which is a temperature responsive device. The thermostat 11 may take any of several forms and has been shown as including generally a base 12, a stack 13, a rivet 14, a bimetallic member 15, contacts 16, and an adjusting screw 17. The contacts 16 are carried on flexible contact carrying members 18 and 19 and the adjusting screw 17 is threaded in and movable relative to the base 12 and passes through an aperture in the member 18 to bear against and adjustably move the member 19. This provides relative adjustment between the contacts 16.

The bimetallic element 15 carries an insulator button 22 to bear against and move the contact carrying member 18 to provide relative movement between the contacts 16 in response to changes in heat applied to the bimetallic member 15.

As best shown in Figure 2, one end of each of the members 15, 18 and 19 is mounted in the stack 13 with a shank 23 of the rivet 14 passing through a hole in each of these members. Terminals 24 are positioned in contact with each of the members 18 and 19 in the stack 13, and insulator washers 2.5 are also provided in the stack 13 to mutually insulate the contact carrying members 18 and 19. In the case shown, the insulator washers 25 insulate the contact carrying members 18 and 19 from the shank 23.

The rivet 14 has a first head 23 which is a composite head, and also has a second head 29. This second head may be spun over or pressed over the top of the base 12 to hold together the elements in the stack 13. The first head 28 has a first part 31 and a second part 32. The first part 31, as best shown in Figure 3, is integral with the shank 23 and this Figure 3 shows the rivet 14 before its assembly as a composite rivet. The shank 23 and first part 31 of the head 28 may be made of steel or other suitable material as is customary in the industry. The second part 32 of the head 28 is made of a metal of good conductivity relative to steel, and aluminum and copper are two such materials which have been found to be quite satisfactory. As shown in Figure 2, the aluminum washer or second part 32 has a stepped inner bore of first and second portions 33 and 34, respectively. The first portion 33 of the bore has a diameter substantially equal to the diameter of the first part 31 of the head 28 and has a depth substantially equal to the axial thickness of this first part 31 to receive this first part 31. The axial thickness of the first part 31 may be slightly less than, but generally in the same order of thickness, as the wall thickness of the shank 23. Also, the radial dimension of the first part 31 outboard of the outer diameter of the shank 23 may be approximately equal to the wall thickness of the shank 23 although this is not essential. It has clearly been found that this first part 31 may be made quite small in both axial and outboard radial dimensions and still operates satisfactorily to resist the tension and compression forces to which the rivet 14 is subjected.

The second portion 34 of the stepped bore has a diameter equally substantial to the outer diameter of the shank 23 to be received on this shank. This stepped bore 3334 is of such proportions as to form a contact surface which is complementary to and interfitting with the outer surface of the shank 23 and first part 31 so that a first outer planar surface 36 on the first part 31 is substantially coplanar with a second outer planar surface 3: thickness of the high conductivity .washer 32 may ,be in the order of two to three times that of the axial thickness of the first part 31. Also, the thickness of the high conductivity washer 32 may r-be at least 'twice theWW Elll thickness of the rivet shank 23:"

The =use--of -either copper--or-aluminum fQr the high conductivity washer 32 permits a method of -assemblyobf the composite riv'et 14 which has additional -advanta'ges.

The two *parts' bf'the composite-rivet -14; as' shown' irr'Fig i ure=3,-- may beassembl'ed by'rmerely:placing tth two' pa'i ts in-a press and pressing zthefirst 'part 51-, which is an integralhead=- on the rivet shank 23;'- untilthis first part has been pressed into this highiconductivitytwashe'r' 32"." The aluniinnm or coppefi'm'aterial} for example; i Oran-e washer'BZ; being'considerab'ly softer-than'=th" steelshank; permits =thisdeforma tion.'- This pre's'siiig operation 'also' assures *that the=stepped' bore 33 3 f'is just exactly -the right'size to receive the: first part 31" of the head'- without any excess clearances This not*only= assures good"heat transfer from -the first part 31 to thehi'gh conductivity washer 32" but also slightly compactsthe meta'hofthe high conductivity Washer 32 in the area 38 "so that it is more dense to thus more effectively resist compression forces'therein.

The rivet 14 may be considered a-st'ress'm'ember and initially as a tension stress in the shank 23' caused by compressing thestack 33' and pressing 'overthe' seeend' head 29 agai'nst the base 12 to holdallthe' elementsin the stack 13.; When the compression force is releasedonthe stack 13, this p'lacesa tensile stress'on the' shank'23L'" This tensile stress is resisted by compression in the area 38"ofth'ehigh conductivity Washer 32. As shown in Figure -2, the entire thermostat may be mounted-against' a mounting surface 39 of an appliance 40 which may be an electrical heating appliance electrically controlledby the cntacts-16. The heat of the appliance '40 therefore is at' the mounting surface and must be transmitted'to the bimetallic member-15 effectively in order to"op erate" the thermostat 11. The high conductivity washer 32'per forms this function providing a good heat transfer from the-mounting surface 39 to the bimetallic member 15i- The rivet 14 still retains the steelshank 23 'to' resist com pression forces caused when a mounting member such'as a 'bolt42 is passedthrough the hollow 'shank 21 3'into 'a tapped hole'43 in the appliance40. When the the'rmoistat is mounted onthe appliance as shown'in 'Figure- 2,' the outer planar surface 37 of the high conductivity'washer i 32 is contiguous with, that is, in contact wands-mam; ingsurface 39 and at'the same time this'highconductivity' washer'32 is contiguous with the bimetallic'membe'r '15k This-provides a very good hea'texchangefromthe'ap pliance 40to the bimetallic'member In practice thermal response tests have shown the'im prov'ementcaused by this high conductivity "Washer 32 as'compared t0 the prior art style'of thermostat wherein thecntire first head 28 'wasmade of steel and integral with the'shank 23. Such thermalresponse'testshave shown that a thermostat of the 'prese'ntinvention'. ha s a temperature differential between oifand"0n""'con dit ions almost exactly one-half that of the temperature differentialof an all steel head28. Also, the initial'overshoo't is about one-half, with initial overshoot'beingfdefined'as a condition wherein if the appliance is initially heated from room "temperature to theoperating temperature,"it passes" the preset operating temperature about which subsequent oscillations of temperature fluctuate "as a mean. This initialover shoot is in most all cases greater than the s'u'bsequent fiuctuationsjcaused'by the off and on conditions of"thecon'tacts-16 because ofthe' thermal "lag" in'all of the metal-parts ambient to the" therniostatand appliance The-compbsite rivet thus-hasa higH COiidIictivity hea for ve'ry "good thermal response, yetretainsflhe steel" shanktor'streng'th. This composite rivet is therefore practica'l' in nsefwhereas it would be' impracticaTif-the entire rivet wremade from high condfictivity' mtal whiicli 'ifi nurrreroifis chan'ges in thedetails ofconstruction' and the combination and arrangement of part's may be resorted to without departing from the spirit and "the scope of the invention ashereinafter claimed.

What is claime d'isr 1. A stress member for a condition responsive device, comprising, a shank, a composite head on one end of said shank formed of first and second parts, said first part-'being'at'tached to said shank and composed ofessentially thefiarhmaterial, a contactsurface on said first partg sa'i'd second part being of good heat conductivity" relative "to-" said first part and having a surface 'complemeiit-ary" to said contact surface for 'interfitting engagement with said first part, whereby'said stressmemb'e'r may be assembled in'a condition responsive device wi'tli" a su'rface of-"sa'id' second part co-planar with a su'rfaceof said first partand contiguous to a condition responsive element the reiilf' 2. A stress member for a thermostat, comprising, "a sha'nk, a composite head on one end of said shank formed 5 of first and'secbnd parts, saidfirst partbeing attached to" said shank andcomposed of essentially the same-material, saidse'cond part being of good heat' conductivity relative to said first part and having a stepped inner bore of first" and se'c'ond' portions; said first portion having a diameter substantiallyequ'al t-o the diameter of said first part and" having a depth substantially equal to-theaxial thickness of said" 'first part to receive same, said second portion" having -a diameter substantially equal to'the outer di ameter 'of said shank, whereby said stress-member may be assembled in a thermostat with said second part con-- tiguous to' a temperature responsive element therein.

3. Arivet'for a thermostat,comprising,a metal shanlq an integral head on one endof said shank, a washer'of good heat conductivity relative to saidshank and having"- astepped'inne'r bore of first and'second portions, said first 'portionhaving a diameter substantially equal to th'ef diameter-"of said head i'andfhavi'n'g a depth substantially' thickness: to "receive said' head, said: ga diameter substantially equal to theouter di'ameter or said shank, 'whereby said rivet may be assembled in a thermostat'with' said Washer contiguous" to a bimetallic 'element"therein and contiguousto an appliance 'toWl'iich thethermostat may be fastened "with good heat conductivity from the appliance to 'thebirnetal lic element of thethermostatpro'vided by said"washer.

{15A "rive't' for "anelectrical thermostat, 'co'mprising,"'a steel shank ofa given 'wallthicknes's, an integral head" on one end' of said shank, said head having 'anaxial" thickness approximating said given Wall thickness; a

washer of good'heat' conductivity relative to steeland having a stepped inner bore of first and second portions,

said firstportion having a diameter substantially equal to the diameter of said head and having a depth sub? stantially equal to said axial thickness to receive said" head, said's'econd portion having a diameter substantially 3 equal to the'outer diameter of said shank, whereby said riv'et maybeassembled in a thermostat with said washer contiguous to a bimetallic element therein and contiguous to'a'nappliance to which the'thermostat may be fastened withgodd heat conductivity from the appliance tothe'bi metallicelement of the thermostat providedby said washer.

5 A hollow rivet for the stack ofan electrical thermostat, comprising, a hollow steel shank-ofa givenwall thickness, a first integral head on one end of said shank asrrsro and having a radial dimension outboard of the outer diameter of said shank approximately equal to said given wall thickness, said first head having an axial thickness approximating said given wall thickness, an aluminum washer of good heat conductivity having a stepped inner bore of first and second portions, said first portion having a diameter substantially equal to the diameter of said first head and having a depth substantially equal to said axial thickness to receive said first head, said second portion having a diameter substantially equal to the outer diameter of said shank, whereby the shank of said hollow rivet may be asembled through elements and the base of the thermostat with said aluminum washer contiguous with said first head and a bimetallic element of said thermostat and a second head may be formed on the opposite end of the shank to hold such elements in place and a mounting screw may be inserted through the hollow rivet to fasten said thermostat to an appliance with good heat conductivity from the appliance to the bimetallic element of the thermostat provided by said aluminum washer.

6. A hollow rivet for the stack of an electrical thermostat, comprising, a hollow steel shank of a given wall thickness, a first integral upset head on one end of said shank and having a radial dimension outboard of the outer diameter of said shank approximately equal to said given wall thickness, said first head having an axial thickness approximating said given wall thickness, an aluminum washer of good heat conductivity received on said shank and pressed onto said first head to have a stepped inner bore of first and second portions, said washer having a thickness in the order of two to three times that of said axial thickness of said head, said first portion having a diameter substantially equal to the diameter of said first head and having a depth substantially equal to said axial thickness to receive said first head, said second portion having a diameter substantially equal to the outer diameter of said shank, whereby the shank of said hollow rivet may be assembled through elements and the base of the thermostat with said aluminum washer contiguous with said first head and a bimetallic element of said thermostat and a second head may be formed on the opposite end of the shank to hold such elements in place and a mounting screw may be inserted through the hollow rivet to fasten said thermostat to an appliance with good heat conductivity from the appliance to the bimetallic element of the thermostat provided by said aluminum washer.

7. A thermostat, comprising, a temperature responsive member, a stress member having a shank and a head and holding said temperature responsive member in said thermostat, said head on said stress member being of a metal of considerably better heat conductivity than said shank, said head being positioned contiguous to said temperature responsive member, whereby, upon fastening said thermostat to an appliance by a mounting member, said head is also contiguous with said appliance.

8. A thermostat, comprising, a base, a rivet, a bimetallic member, a stack in said thermostat including said rivet, base and one end of said member, a hollow shank on said rivet, first and second heads on opposite ends of said rivet, said second head being positioned against said base to hold said stack and the elements carried thereby firmly relative to said base, said first head having first and second parts, said first part of said first head being integral with said shank, said second part of said first head being of a metal of considerably better heat conductivity than said shank, said second part having a stepped bore to receive said shank in the smaller portion of the bore and to receive said first head in the larger portion of the bore, said first head being positioned contiguous to said bimetallic member, whereby, upon fastening said thermostat to an appliance by a mounting member passed through said hollow shank, said metal washer is also contiguous with said appliance.

9. A thermostat comprising, a base, a rivet, a bimetallic member, a stack in said thermostat including said rivet, base and one end of said member, a hollow shank on said rivet, first and second heads on opposite ends of said rivet, said second head being positioned against said base to hold said stack and the elements carried thereby firmly relative to said base, said first head having first and second parts, said first part of said first head being integral with said shank and having a first outer planar surface, said second part of said first head being of a metal of considerably better heat conductivity than said shank, a second outer planar surface on said aluminum washer, said second part having a stepped bore to receive said shank in the smaller portion of the bore and to receive said first head in the larger portion of the bore to a point whereat said first and second planar surfaces are substantially coplanar and to hold said second part on said first part at least in the axial direction away from said second head, said first head being positioned contiguous to said bimetallic member whereby, upon fastening said thermostat to an appliance by a mounting member passed through said hollow shank, said second outer planar surface of said metal Washer is also contiguous with said appliance to effect good heat transfer from said appliance to said bimetallic member.

10. A thermostat comprising, a base, insulator washers, a rivet, first and second elongated flexible members, an elongated bimetallic member, a stack in said thermostat including said rivet, washers, base and one end of each of said members with said insulator washers providing an insulative mounting for said flexible members relative to each other, a hollow steel shank of a given Wall thickness on said rivet, first and second heads on opposite ends of said rivet, said second head being pressed over against said base to hold said stack and the elements carried thereby firmly relative to said base, said first head having first and second parts, said first part of said first head being integral with said steel shank and having a first outer planar surface, said second part of said first head being of metal of good heat conductivity and considerably softer than said steel shank, said second part having an outer diameter at least twice the outside diameter of said steel shank, a second outer planar surface on said metal washer, said second part being sufiiciently softer to permit same being pressed upon said first part to cause indentation into said second part to a point whereat said first and second planar surfaces are substantially coplanar and to hold said second part on said first part at least in the axial direction away from said second head, said first head being positioned contiguous to said bimetallic member, whereby, upon fastening said thermostat to an appliance by a mounting member passed through said hollow shank, said second outer planar surface of said metal washer is also contiguous with said appliance to effect good heat transfer from said appliance to said bimetallic member.

11. A thermostat comprising, a base, insulator washers, a rivet, first and second elongated flexible contact carrying members, an elongated bimetallic member, a stack in said thermostat including said rivet, washers, base and one end of said members with said insulator washers providing an insulative mounting for each of said flexible members relative to said rivet, a hollow steel shank of a given wall thickness on said rivet, first and second heads on opposite ends of said rivet, said second head being pressed over against said base to hold said stack and the elements carried thereby firmly relative to said base, said first head having first and second parts, said first part of said first head being integral with said steel shank and having a first outer planar surface, said sec- 0nd part of said first head being of aluminum of good heat conductivity and considerably softer than said steel shank, said second part having an outer diameter at least twice the outside diameter of said steel shank and a thickness at least twice the said wall thickness of said ste'el 's'liahk, a second outef'planalr' surface on 'said alu niiiiiimvvasherg said second part being sufiicientlysofter' to perrnit same being pressed upon said first'part'to cause indentation into saidseco'nd part 'to a point Whereat said first and second planar surfaces are coplanar and to hold said 'secondpart' onsai-d first part at least'in'tlie axial dire'ction aWay fro 'rn' 'sa'id second 'head, said first 'head being positioned contiguous to said bimetallic niernber; whereby; upon fa'ste'ning said thermostat to an appliance by a mounting mernbe'r passed through said hollow shank, said'second outer planar surface of said aluminum washer is also contiguous with said appliance to effect good heat transfer from said appliance to said bimetallic member,

and sa'id' steel shank has suflicie'nt strength to resist any tension "and compression fo'rce's'" therein.

12'.'A"stress member for a 'therriiost'at,'comprising, a shank, a composite head on one erid of's'aid'shank formed of'fir's't and'sec'on'd parts'fsaid first part'being attached to saidshank and composed of essentially the same Inaterial, said second part" being 'of 'good'he'at' conductivity relative to said fir's't' part and having 'a'pcrtion'inter fitting with said first partpa first contact surface on said first partfand a secon'd contact surface on said second partho'planar with said firs't -contactsurface; whereby said stress member may be assembled in' 'a thermostat withflsaid first and "second contact sur'fa'c'es contiguous to a temperature responsive eleinent' therein 4 13'.A"riv'et for a thermostat' having a biniet'allic' 'ele'-' ment and for use in an appliance in which the therniostat" I may be fastened, said rivet comprising 'a in'etalshank, an

integral head onon'e end of said'shank,' a washer of 8 v go o dheat" coiiduictivity relativyto saidpsha'nk 'and having a'poftiondntei'fittingwith said head, first and second coplaii'ar' cont'a'ct"surfaces on said' head 'and said wa her respectiv ly, wherebyfsaid rivet maybe assembled in a thie'rmos'tatfivithsaid washer contiguousto'one of said bi'r lf talli'c 'ele'rne'fifan d said appliance, arid vvith said finsfi and secofid con ct surfa cesicontiguous'to the other of said birnet'allic eleiiient an d said appliance in which the tlieirhostat"rnay" b"fastened ivith 'good' heat conductivity 'frdin appliance to the bimetallic element of the therino'stat'provided by 'said Washer.

14. Interim-"a thermostat having a bimetallic el'e nie'nt an'd'jfor' use'in'anappliance, comprising, a metal" shank, an integral head on one end of said shank, a washer of good haficondu'ctivity relative to said shank and thermostatin'ay b fastened with good he'at conductivity from the"applianceto the bir'nctallic element of the thermostatpfdvid'edby said Washer.

Rafei ences Cited in the fileof this patent UNITED STATES PATENTS 2,5671% Weila'nd Sept. 4, 195 1 2,702,215 1 Chin'n" Apr. 26, 1955 2,718,572 Harris; Sept. 20,'19ss- 

